Perform .join on value in array of objects

If you want to map objects to something (in this case a property). I think Array.prototype.map is what you're looking for if you want to code functionally.

(fiddle)

If you want to support older browsers, that are not ES5 compliant you can shim it (there is a polyfill on the MDN page above). Another alternative would be to use underscorejs's pluck method:

var users = [
      {name: "Joe", age: 22},
      {name: "Kevin", age: 24},
      {name: "Peter", age: 21}
    ];
var result = _.pluck(users,'name').join(",")

I've also come across using the reduce method, this is what it looks like:

console.log(
    [
        {name: "Joe", age: 22},
        {name: "Kevin", age: 24},
        {name: "Peter", age: 21}
    ]
    .reduce(function (a, b) {
        return (a.name || a) + ", " + b.name}
    )
)

The (a.name || a) is so the first element is treated correctly, but the rest (where a is a string, and so a.name is undefined) isn't treated as an object.

Edit: I've now refactored it further to this:

x.reduce(function(a, b) {return a + ["", ", "][+!!a.length] + b.name;}, "");

which I believe is cleaner as a is always a string, b is always an object (due to the use of the optional initialValue parameter in reduce)

Edit 6 months later: Oh what was I thinking. "cleaner". I've angered the code Gods.

Well you can always override the toString method of your objects:

    var arr = [
        {name: "Joe", age: 22, toString: function(){return this.name;}},
        {name: "Kevin", age: 24, toString: function(){return this.name;}},
        {name: "Peter", age: 21, toString: function(){return this.name;}}
    ];
         
    var result = arr.join(", ");
    console.log(result);